The present invention relates to coupling systems for transmission of fluids, and in particular to coupling systems for attaching a conduit for high temperature fluid to a housing in such a way that heat is not transferred from the high temperature conduit into the housing.
One environment in which such coupling systems has become important is the automotive industry. As part of the current trend of manufacturing automobiles with lighter construction, utilizing aluminum instead of steel, and plastic instead of metal and so on, it has become increasingly popular for designers to replace more and more metal parts with parts made from plastic material. Only recently, however, has it become possible to replace metal automotive engine components with plastic components, because of the various strength, durability and heat resistance characteristics which the particular components must possess. While high strength, high heat resistant plastic and ceramic materials do exist, such materials are extremely costly and are sometimes brittle, and are therefore not economically feasible. However, certain engine components can be replaced, if they are low strength requirement components which can be effectively isolated from high heat and temperature sources. These particular components can then be manufactured from relatively inexpensive thermoplastic materials such as ABS. Such inexpensive plastic components must be protected from temperatures that are in excess of approximately 350 degrees Fahrenheit.
One such automotive engine component which, among others, can be manufactured from inexpensive plastic material, if properly isolated, is the air intake manifold. Through the use of the proper gasketing or other suitable isolation technique, the main body of an air intake manifold housing can be effectively substantially thermally isolated from the remainder of an engine block. However, there exists one feature which is becoming increasingly prevalent in modern, fuel efficient, low emission engine, which presents particular difficulties with respect to isolation from heat. In order to improve the fuel efficiency and emissions quality of automobile engines, it has become common practice to direct hot exhaust gases from the exhaust manifold into the intake manifold, in order to elevate the temperature of the incoming air to improve the efficiency of the combustion process, as well as to combust unused fuel vapor which exists in all automobile exhaust. However, while the ambient air which is brought in to the air intake manifold may be, as much as 125 degrees Fahrenheit, the exhaust gases which are being recirculated in to the air intake manifold may have a temperature as high as 1300 degrees Fahrenheit. Such extreme temperatures would lead to the destructive transmission of heat from the exhaust gas recirculation (EGR) tube, which must be made of metal, into the portions of the housing to which the EGR tube is attached. Low temperature plastics would quickly begin to degrade or even melt or burn under prolonged exposure to such heat unless properly insulated from the EGR tube.
Various attempts have been made to provide for inexpensive adequate insulation between the hot EGR tube and the plastic housing. One such proposed solution is to provide a metal flange which centers the hot tube end within a much larger aperture in the housing. The flange, often in the shape of a cup, is then affixed to a cylindrical collar which extends from the housing, surrounding the aperture. However, since the flange or cup is manufactured from metal, the heat is simply transferred through the flange into the portion of the collar which makes contact with the flange. Although this transferred heat is slightly less intense than at the extreme end of the EGR tube, the transferred heat is still sufficient to cause the premature degradation and/or melting of the plastic surfaces which are in direct contact with the flange. Accordingly, it has been the practice to provide that portions of the plastic collar are replaceable and separable from the main housing body. Such replaceable portions are, in fact, designed to degrade and be replaced on a regular basis. Such a construction is undesirable from the standpoint of the cost and inconvenience of replacement of the removable portions.
Another proposed solution is to position a cylindrical insulator body between the hot EGR tube end and the collar portion of the housing. However, to provide significant effective insulation capabilities, high performance insulating materials must be used, as previously described, which are prohibitively expensive, and as well, may have other undesirable performance characteristics, such as brittleness, low durability, susceptibility to fatigue and so on.
It is accordingly desirable to provide a system for coupling a high temperature tube or conduit to a housing in such a way that the heat from the high temperature conduit is not transferred into the material of the housing itself, so that the housing may be manufactured from common or at least non-high performance material.
Another object of the invention is to provide such a thermal isolation coupling system, in which the actual coupling components themselves may further be fabricated from relatively inexpensive, low temperature, low performance materials.
These and other objects of the invention will become apparent in light of the present Specification, Claims and Drawings.